286 



ME. T. 0. BOSWOETH ON THE 



[June 191 2, 



For example, an inclination of 15° would be thus produced in 

 strata resting against a 35° rock-slope, if the marl were to contract 

 to three-quarters of its former thickness (see fig. 2, below). 



Fig. 2. 



\ 



ko 



P 



^^7^6* 









^^ 



"^ 



P^ 





•^ 



1 



L 





Let P be a bedding'-plane and let the thickness 





of marl beneath it 



shrink from P Q to P^ Q 





Then R= - 



P P^ tan e 

 p Q tana 





/. tan 



= R tan a 



The above-described inclination resulting from deposition upon 

 rock-slopes is conveniently referred to as tbe 'tip' of the strata. 



Petrography of the Upper Keuper. 



In this section of the complete paper it is shown that a con- 

 siderable variety both of red and of grey rocks occur, and certain 

 types characterize certain horizons. 



One important variety of grey rock described as quartz ose 

 dolomite may be mentioned here. This occurs chiefly in the 

 upper half of the Keuper Marls, as thin seams often less than half 

 an inch thick. It is a very hard compact rock of semicrystalline 

 appearance, composed of fine angular sand, dolomite rhombs often 

 accompanied by barytes, and some fine argillaceous matter. 



The composite character of the grey bands is discussed, and it is 

 pointed out that usually they contain one or more porous seams 

 with grey marl above and below, some of which was originally red 



